1. Field of the Invention
The present invention relates to ultrasonic transducers of the type employed on automatic wire bonders. More specifically, the present invention relates to self isolating mounting structures for mounting ultrasonic transducers onto automatic wire bonders with a minimum loss of energy.
2. Description of the Prior Art
Ultrasonic transducers have been used in the semiconductor industry on automatic wire bonders used to make fine wire bonds that connect pads on semiconductor devices to lead frames or carriers. Heretofore it was known to manufacture a mounting flange for a transducer as an integral part of the transducer so that it would be precisely located at the theoretical node or zero displacement point of the transducer. This zero node would couple the least amount of energy into the automatic wire bonder on which it was mounted.
It has been observed that the impedance of individual transducers when mounted on different automatic wire bonders displayed different values of characteristic impedance Z.sub.M. Heretofore, it was assumed that the coupling between the transducer mounting flange and the bonding head was the main cause of the change of this impedance Z.sub.M and that a tight coupling would eliminate the differences between transducers that were manufactured to identical specifications and tolerances.
A series of identical transducers were manufactured and tested to determine the type of mounting and/or coupling which would reduce the mounting impedance Z.sub.M and also provide uniform mounting impedance. These series of tests confirm that the coupling between mounted transducers varied such that large impedance changes were noted between the same transducer when mounted on different bonding heads.
It was further discovered that stress at the interface coupling played a large role in determining whether the coupling could be made tight and consistent so as to reduce the mounting impedance Z.sub.M.
Heretofore prior art transducers were assembled using matched components to achieve a predetermined desired impedance and frequency. It was often necessary to assemble and reassemble components several times in order to achieve the desired results.
It would be desirable to provide a self isolating transducer that enabled the mounting flange to be tightly coupled to a bonding head and which reduces the bonding impedance and eliminates the impedance variations and differences that occur when a standard ultrasonic transducer is mounted on different bonding heads.